Method for producing a high strength ferrous metal



United States METHOD FOR PRODUCING A HIGH STRENGTH FERROUS METAL WilliamB. Larson, Birmingham, Robert F. Thamson, Grosse Pointe Woods, and FredJ. Wehhere, @rchard Lake, Mich, assignors to General Motors(Iorporation, Detroit, Mich., a corporation of Delaware No Drawing.Filed Dec. 29, 1958, Ser. No. 783,144

'8. Claims. (Cl. 75-130) present invention, describes and claims animproved ferrous metal composition which provides castings havingoutstanding mechanical properties. These properties result from the factthat substantially all of the hypereutectoid carbon is present as freegraphite in a compacted or roughly spheroidal form with practically nohypereutectoid carbide being present. In order to obtain this desirablemicrostructure, specified small amounts of carbon, silicon, and boronmust be present in the metal, and the melt is preferably also inoculatedwith tellurium and/or bismuth.

The cast ferrous product described and claimed in the aforementionedWhite et al. patent application possesses outstanding mechanicalproperties in both the as-cast and heat treated conditions. For example,castings formed from this material have, in the as-cast condition, amodulus of elasticity of at least 27.5 p.s.i., a minimum tensilestrength of 80,000 p.s.i., and a yield strength of at least 60,000 psi.at 0.2% ofiset. In some instances the modulus of elasticity is as highas 29x10 p.s.i., while the tensile strength ranges up to about 90,000psi.

However, we have found that even the preferred composition disclosed inthe White et al. patent application without the aforementionedinoculations may solidify in .a wide range of microstructures.

These microstructures vary from all gray iron containing flake graphiteand some isolated compacted graphite in one extreme to all white ironwith no free graphite on the other. This variation is believed to be theprimary cause of the different amounts of residual iron carbide observedafter inoculation.

Accordingly, it is a principal object of the, present invention toeliminate any inconsistency in the microstructure of this type offerrous metal. A further object of this invention is to provide a methodof producing a ferrous metal product which always possesses theaforementioned desirable mechanical properties and micro- .structurewithout the necessity of inoculating the melt with tellurium and/orbismuth. A still further object of our invention is to provide a simpleand inexpensive process for forming such a ferrous metal alloy in whichthe desired microstructure may be consistently produced,

thereby insuring that all castings have the same outstanding mechanicalproperties.

These and other objects are attained :in accordance with this inventionby a process in which the boroncontainingmoltenferrous metal in.eachheat is brought line to the same metallurgical condition. This isdone prior to inoculation with tellurium, if tellurium is .to be added.Specifically, the desirable microstructure and mechanical properties ofthe ferrous metal are obtained by superheating the base metal at atemperature of approximately 2900 F. to 3100 F. for a short period oftime prior to tapping and inoculation, if the latter is employed. Asuperheat temperature of 2950 F. to 3000 F. is generally preferred.Also, desirable agitation can be provided by lancing or flushing themelt, which is preferably also superheated, with a dry gas to produceturbulence. The latter procedure considerably reduces the necessaryholding time at superheat to produce the desired microstructure.

Superheating the melt to the foregoing temperature in accordance withour invention eliminates the necessity of inoculating the melt withtellurium and/or bismuth in most instances and still provides castingswhich consistently contain free graphite in compacted form without thepresence of any appreciable amount of iron carbide or flake graphite.Moreover, we have now found that a preferred microstructure can beobtained with the process described herein at a lower silicon contentthan was heretofore possible. For example, excellent results areprovided with a ferrous metal of this type which contains only about1.5% silicon. The resultant castings have improved as-cast strength andductility.

As indicated above, this new steel-like material, which has asubstantial amount of graphite in the as-cast condition, contains acontrolled amount of boron as well as silicon and carbon. Thecomposition is such that the metal normally would solidify as a whitecast iron if no boron were present; that is, in the absence of boron thecarbon will be present in the combined form rather than as free carbon.On occasion, it may be desirable to include a small amount of telluriumand/or bismuth in the melt. At the present time tellurium is preferredover bismuth as an inoculant because it appears to produce superiorresults.

The various constituents in the cast ferrous metal, of this inventionare so balanced that free carbon separates out of the cast product incompacted form, generally similar to the temper carbon of conventionalmalleable iron, rather than in flake form as in ordinary gray cast iron.In general, the ingredients of the new cast material are present inamounts to provide a ferrous base metal comprising approximately 1% to2.5% carbon, 1.5% to 3.2% silicon, manganese not in excess of 1.15%,0.001% to 0.02% boron and the balance substantially all iron. Foroptimum results, the carbon content should be between 1.5% and 1.9% andthe silicon content approximately 2% to 2.6%. V

When tellurium is employed, it should not be present in an amountgreater than about 0.01%, a tellurium addition of about 0.003% to 0.008%being preferred. A tellurium content exceeding 0.008% results in atendency to produce chill in thin sections. This result of using highertellurium contents is of particular interest since the preferredcomposition set forth above is not highly section sensitive in thatthere is only a slightly greater tendency for hypereutectoid carbideformation in thin sections than in heavy sections. If bismuth ratherthan tellurium is used, as much as 0.02% of this material may be used.Although both tellurium and bismuth may be present at the same time, thetotal amount of these constituents should not exceed approximately0.02%.

Of course, sulfur is normally always present in cast iron and steel, andthis constituent is not detrimental to the resultant product inquantities even as large as 0.5%, provided the metal also contains asufiicient amount of manganese. Usually, however, about 0.3% is themaxi.-

mum amount of sulfur normally found in such ferrous metals. Themanganese counteracts the detrimental effects of sulfur by combiningwith it to form manganese sulfide.

Accordingly, it is desirable to have a sufficient amount of manganesepresent to combine with the sulfur, but an excess of either of theseconstituents is detrimental since it results in undesirable carbidestabilization. The preferred manganese content should satisfy theequation Mn=1.7 (percent sulfur)+0.2. In practice, sulfur will always bepresent, and the sulfur content usually is at least 0.02% unless aspecial procedure is employed for reducing the amount of sulfur.However, manganese sulfide functions as a chip breaker in machiningoperations and thereby improves the machineability of the resultantcastings. It also appears that the presence of sulfur may somewhatimprove the fluidity of the molten cast metal. From the standpoint ofthe present invention, manganese does not appear to be necessary if nosulfur is present.

A cast ferrous base metal having the following composition appears topossess optimum physical properties: 1.5% to 1.9% carbon, 2% to 2.6%silicon, 0.3% to 0.8% manganese, 0.05% to 0.2% sulfur, 0.005% to 0.015%boron and the balance iron. However, for some applications it may bedesirable to include as much as 0.05% boron and to use tellurium in anamount as small as 0.001% or as large as 0.01%. If bismuth issubstituted for tellurium, the preferred range is between 0.005% and0.01%. tained using an as-cast malleable iron consisting essentially of1.7% carbon, 2.25% silicon, 0.4% manganese, 0.1% sulfur, 0.01% boron,0.05% phosphorus and the balance iron.

Of course, the impurities normally found in cast iron may be present inthe usual small amounts. In addition to the elements listed above, theferrous base product of the present invention also may contain one ormore of the various elements which are frequently present in cast ironeither as impurities in small quantities or as intentional additives inlarger, controlled amounts when particular properties are desired. Theseelements include chromium, nickel, copper, titanium, aluminum, vanadium,molybdenum, tin, etc.

It should be noted that the high silicon content and the low carboncontent of this new ferrous base material are just the reverse of theproportions of these elements normally used in cast irons. tion, inconjunction with the presence of boron and the application of superheat.which imparts to the resultant product its high modulus of elasticityand outstanding versatility.

While it is possible to produce compacted graphite in castings havingcompositions within the broader ranges recited above, the narrowerranges are preferred in order to produce optimum results. The lowcarbon, high silicon composition, such as one containing 1.80% carbonand 2.25% silicon, has been found to be peculiarly susceptible to theformation of compacted graphite when processed according to the presentinvention. Deviations from the preferred analysis may result in usefulbut less favorable structures. For example, in some instances sectionsensitivity is encountered with compositions outside the narrow rangeslisted above. Moreover, the higher carbon or lower silicon levels whichapproach those of conventional malleable iron produce a correspondingincrease in hypereutectoid iron carbide. Although this carbide may besubstantially eliminated by raising the silicon content or byinoculation with various graphitizers, such procedures frequentlyproduce some flake graphite, particularly in heavy sections of thecasting. As is true with conventional pearlitic malleable iron andso-called ductile cast iron or nodular iron, the presence of flakegraphite or hypereutectoid iron carbide reduces the strength andductility of the metal. Tensile tests indicate, however, that thepresence of Excellent results have been obu It is this uniquecombinasome small hypereutectoid carbide particles randomly distributedthroughout the metal is much less detrimental to mechanical propertiesthan the presence of flake graphite. Acceptable strength and ductilitycan be obtained with this improved ferrous metal in both the as-castcondition and in the heat-treated condition even when some carbide ispresent in this form. While we have found that the presence ofapproximately 5% by volume of Type D graphite may lower tensile strengthby 20,000 psi. and reduce the ductility drastically, we have also foundthat the presence of stubby flakes or quasi-flake graphite in smallamounts generally has no appreciable effect on either tensile strengthor ductility. It appears that if the base iron melt having the preferredcomposition is a type which would solidify as only white iron with nofree carbon being present, the inclusion of boron alone would produce astructure having of the free carbon in the form of compacted graphiteand which contains no residual hypereutectoid iron carbide. Superheatingthe melt at a temperature of 2900" F. to 3050 F., however, insures sucha structure regardless of the structure of the base iron without boron.

If the retained boron is present in a quantity greater thanapproximately 0.02%, some stabilized hypereutectoid carbide will beproduced. Consequently, the addition of excess boron does not compensatefor the deleterious effects produced by too high a carbon content.Chemical analysis has indicated that when the preferred compactedgraphite structure is obtained, more than twothirds of the total boronis present as acid-insoluble boron, while an increased amount of Type Dflake graphite with less compacted graphite is associated with anincrease in acid-soluble boron. It therefore appears that the formationof compacted graphite is correlated with the presence of anacid-insoluble boron compound. The acid solubility of the boron in themetal was deter mined by standard analyses using a solution of 20%sulfuric acid or phophoric acid.

Although boron is the essential ingredient which produces compactedgraphite in the composition described herein, the use of superheatinsures against the formation of flake graphite. Regardinghypereutectoid iron carbide, it is generally desirable to reduce theamount of this compound to less than 1% of the volume of the metal,although for some applications the carbide content may range up to 5% orhigher. However, it is much more diflicult to machine the cast productwhen it contains more than about 2% hypereutectoid iron carbide.Nevertheless, the presence of this carbide contributes measurably to thewear resistance of the metal, and consequently a hypereutectoid carbidecontent as high as even 10% by volume may be desirable in applicationswhere high wear resistance is an important factor. As indicated above,the present process applied to the preferred composition consistentlyproduces a cast ferrous base metal which contains less than 1%hypereutectoid carbide.

This metal may be prepared by various melting processes employed inmaking conventional iron castings. Direct arc melting and high-frequencyinduction melting are among the specific procedures which have beensuccessfully used. Likewise, either batch-type or continuouscupola-direct arc duplcxing operation may be employed. The process forproducing the ferrous base metal appears to be independent of thefurnace lining used. Heats have been successfully melted in furnaceslined with SiO (acid), MgO (basic) and zirconium silicate (neutral).Tapping and pouring temperatures of 2750 F. to 2850 F. and 2600 F. to2700 F, respectively, provide satisfactory results. These temperaturesare consistent with current malleable iron practice. However, thetapping temperature may range from about 2700 F. to 3000 F. underparticular conditions, and the pouring temperature may be as high asapproximately 2750 F.

Apparently because of the low carbon content of the oxidize the metal.

metal, melting .in direct arc furnaces frequentlyresults in someporosity due to occluded gas. This condition can be avoided by meltingthe metal under a protective slag.

The optimum carbon content of approximately 1.8% may be obtained by amixture of plain carbon steel and conventional white iron, such as aniron containing 2.6% carbon, 1.4% silicon, 0.35% manganese and 0.1%sulfur. When melting in induction furnaces, it is convenient to mixwhite iron scrap with the steel and to melt these two metals together.On the other hand, when a direct arc furnace is used, it appearsdesirable to transfer the molten iron from the cupola to a direct arcfurnace and to subsequently add an appropriate amount of slag. Themolten steel, which has previously been melted in a second direct arcfurnace, is then mixed with the cupola metal. Such a procedure providesconsistent chemistry control due to minimum oxidation loss and alsoconstitutes a convenient means of preventing gas pickup.

Cold melting by direct arc is also possible, but the higher carboncontent white iron should be melted and a fluid slag obtained prior toadding steel. In either direct are or induction melting, silicon andmanganese may be added to the metal at any stage.

We have also found that the desirable low carbon content may be producedby employing an oxygen jet converter type of arrangement to reduce thecarbon content of conventional cupola melt malleable iron. Arefractory-lined vessel and a water-cooled copper lance maybe used. Bycarefully controlling the chemistry and quantity of the hot charge andmetering the oxygen, it is possible to accurately predict thecarboncontent of the melt at any time during the blow, Silicon and manganesecan be added to the receiving ladle upon tapping of the melt in order tocompensate for losses which occur during the blow and to maintain properamounts of these elements in the melt. These additions also serve to de-If the melt is to be inoculated with boron and/ or tellurium, this maybe .done while tapping the metal from the receiving ladle to a transferladle. However, such a practice .does .not appear to be as economical as.a normal cupola .direct arc duplexing operation.

The importance of a microstructure which is substantially free ofhypereutectoid iron carbide and flake graphite is well recognized in thenodular iron and malleable iron industries. To produce such amicrostructure inaccordance with the present invention, it is necessaryto use the aforementioned amount of boron. However, it is generallyfound that the base metal will have some boron present and, bysuperheating the boron-containing rmelt as described herein, itfrequently is unnecessary to inoculate it with additional boron. Aresidual boron content of approximately 0.001% to 0.003% normally can beobtained from white iron scrap used in the base charge. 1

Ladle additions of boron and tellurium land/or bismuth, if employed,areadjusted according to the composition of a base iron, meltingconditions, .etc. A boron inoculation may be made with a number ofboroncontaining compounds. Among the inoculants which can be employedare ferroboron, boron carbide, calcium boride, nickel-boron, pure boronmetal and anhydrous borax. Tellurium also may be added in various forms,

such as pure tellurium, ferrotellurium or copper-tellurium, for example;and bismuth can be introduced as .sub-

t6 However, in large production quantities where considerable turbulenceis generated, the additive or additives may be placed in the bottom ofthe receiving ladle or introduced into the stream.

When the ferrous metal having the aforementioned composition is heatedto a conventional melting and pouring temperature of about 2700 F. to2800 F. and thereafter cast, the microstructure of the resultantcastings frequently will not show the desired spheroidal or compactedgraphite. On the other hand, when such a metal is superheated to atemperature between approximately 2900 F. and 3050 F., and held at thistemperature for at least 10 minutes, the castings produced have amicrostructure which contains considerably less massive orhypereutectoid carbide. Furthermore, the free graphite has a roughlyspheroidal or compacted configuration quite similar to the obtained byannealing white iron.

It should be noted that superheating the melt at. the aforementionedtemperature results in less retained carbide in the cast structure thanheating an identical melt to only 2800 F. This result is contrary to the.normal concept that superheating cast iron has a de-graphitizing effectbecause it destroys centers of nucleation.

in general, a superheat temperature between 2950 VP. and 3000 F. ispreferred. With a melt which has been induction heated to such atemperature, a holding time at superheat of about 15 to 25 minutes ishighly satisfactory. can be obtained with superheat times as short as 10minutes in an induction furnace, a period of 15 to 20 minutes ispreferable to insure complete compacting of the free graphite. If adirect arc furnace is employed, the time the melt must be held atsuperheat to produce the proper microstructure can be reduced toapproximately 2 to 5 minutes.

As hereinbefore stated, this microstructure can be pro duced at asomewhat lower melt temperature in an induction furnace by agitating themolten metal with dry gas introduced below the surface of the melt. Suchlancing or flushing of the melt to produce turbulence also considerablyreduces the necessary holding time at superheat. Thus it is possible tocombine the superheating and gas treatment to produce a compactedgraphite structure in 2 to 5 minutes at superheat. The result evidentlyis not dependent upon chemical reaction with the gas and may beaccomplished with an inert or reducing gas as well as with an oxidizinggas. However, the gas should be in a dry condition. Examples of drygases which have proved to be satisfactory are air, oxygen, nitrogen,argon, helium, carbon dioxide and ammonia gas, although other dry gasesmay be employed. Gas lancing of the melt appears to be considerably moreeffective in an induction furnace than in adirect arc furnace or theladle. The typical long, narrow induction furnace permits more thoroughagitation of the melt by the gas.

Superhe'ating accompanied by gas lancing produces a predominance ofcompacted graphite without adding tel- .lurium and without the necessityof boron inoculation, provided the base metal contains a sutficientamount of boron. As indicated above, however, a tellurium inoculationfurther helps to eliminate any small amount of flake graphicwh-ich mightotherwise be present and provides for more compact graphite nodules. Inthe absence of superheating, it is quite frequently found that residualflake graphite is present in the solidified boron-containing castings.

When the melt is superheated to the proper temperature, the reactiontime required with gas flushing is very constant, requiring two tofourminutes for pounds of molten metal at a gas flow rate of 20 cubicfeet per hour. This flow rate is equivalent to approximately 0.0145cubic foot of gas per pound of metal. In general, we have found that alancing rate of about 0.01 to 0.03 cubic foot of ,gas per pound of metalprovides satisfactory results.

While the desired microstructure frequently Of course, higher gaslancing rates may be employed, but normally no additional benefits areprovided by gas rates in excess of those hereinbefore listed. Likewise,it is obvious that lower flow rates for the gases may be used whensuperheating is employed in conjunction with gas lancing.

As hereinbefore mentioned, the influence of gas flushing is not due tochemical reaction of the molten metal with the gas, but insteadevidently results fro-m the turbulence created by the gas stream. Theeflect of flushing on induction melts is reduced at lower temperaturesbecause of the decreased fluidity of the melt. Accordingly, aconsiderably longer lancing time is required to provide any beneficialresults at temperatures in the order of 2750 F. to 2800 F. than at thesuperheat temperature of 2900 F. to 3000 F. At the former relatively lowtemperatures, a lancing rate of approximately 0.025 cubic foot of oxygenper pound of melt was required to produce any benefits, while excellentresults were obtained with lancing a melt superheated to 2900 F. with anoxygen flow rate of only about 0.0145 cubic of oxygen per pound of melt.

Unlike purging with the other gases mentioned, an ammonia or ammoniumchloride flush in an induction heated melt appears to result in a moreporous casting. The gaseous condition produced by NH CI and NH evidentlyis largely attributable to nitrogen because we have found that theaddition of about 0.03% aluminum or titanium following a NH lancecompletely eliminates the porosity otherwise produced in the castings.The titanium addition resulted in the formation of titanium nitrides inthe microstructure. Additions of approximately 0.1% aluminum or titaniumwere highly successful in eliminating porosity in castings poured fromdirect arc melts.

If gas lancing is employed, the gas may be introduced by means of asteel tube coated with a suitable refractory, such as an oxide wash.Such a tube can be used in the uncoated condition, but a fired ceramiccoating, for example, reduces any tendency for the tube to melt. Arefractory tube or a graphite tube coated with a refractory also may beemployed, but any ceramic should be preheated before insertion into themelt to prevent cracking from thermal shock. In general, the outlet endof the tube should extend at least six inches below the surface of themolten metal. A tube having an internal diameter of A inch to /2 inch issatisfactory, but the tube may be larger or smaller depending upon theflow rate and the size of the melt. If the flow rate is maintainedconstant, the larger diameter tube is more inclined to become cloggedwith semi-molten metal. Of course, too high a flow rate would actuallytend to blow the metal out of the furnace.

Extreme preferred orientation of compacted graphite can be produced whenpouring temperatures are excessively high due to pouring too soon aftertapping of the superheated melt. High pouring temperatures tend toproduce larger primary austentite dendrites and magnify the segregationof these dendrites and graphite, the last constituent to solidify; andwe have found that a relatively low pouring temperature substantiallyeliminates this condition of preferred orientation of compactedgraphite. Hence it is highly desirable to pour the molten ferrous metalfrom the ladle into the mold at a temperature below 2800 F. In general,pouring temperatures of 2650" F. to 2700 F. are preferred.

Various tests were conducted to determine the mech anism involved in thegraphitizirig eflect produced by superheating. For example, one heat hada composition of about 1.83% carbon, 2.6% silicon, 0.4% manganese, 0.01%boron, 0.09% sulfur and the balance iron. This melt was melted atapproximately 3000" F. in a magnesia crucible, transferred to a ceramiclined ladle, and subsequently poured into a sand mold. Almost all thegraphite was of the compacted type. The iron carbide was aboutcompletely eliminated, even in casting sections having a thickness ofonly inch, by a twenty-four minuteholding time at superheat temperature.

Another heat consisting of about 1.76% carbon, 2.6% silicon, 0.42%manganese, 0.01% boron, 0.1% sulfur and the balance iron was heated to2900 F. It was then lanced with oxygen for one to four minutes with aflow rate of approximately 13 cubic feet per hour. The resultantcastings exhibited a good compacted graphite structure. Optimum graphitedensity and complete elimination of excess iron carbide were obtainedwith only a two minute lancing period.

Other specimens of generally similar composition, which were superheatedat 2900 F. and lanced with argon, were completely free of iron carbideand contained compacted graphite. Similar results were obtained withnitrogen lancing at 2900 F. Hydrogen also was successfully employed, butthe graphite was somewhat less dense than in heats lanced with oxygen,nitrogen or argon.

Tests also show that this ferrous metal composition contains excesscarbide if it is superheated much above 3050 F. For example, one heatconsisting of about 1.6% carbon, 2.6% silicon, 0.35% manganese, 0.01%boron, 0.1% sulfur and the balance iron was superheated for eighteenminutes at 3100 F. with no gas lancing being employed. A relativelylarge amount of carbide was present in the resultant castings,indicating that superheating above about 3000 F. provides no additionaladvantages and superheating at a temperature higher than approximately3050 F. appears to be detrimental.

The steel-like ferrous metal produced by the foregoing processconsistently possesses a tensile strength of 80,000 to 100,000 p.s.i. at2% to 3% elongation at rupture without the benefit of heat treatment.Its modulus of elasticity of 27.5 to 28.5 million p.s.i. is superior tothat of any other known cast iron type of material, including gray castiron, malleable iron, and ductile iron produced with magnesium or rareearth inoculations. These desirable mechanical properties make thismaterial particularly advantageous for applications requiring stiffnessand high strength, such as for crankshafts of gasoline and dieselengines.

The feeding characteristics of the cast ferrous base metal processed inaccordance with this invention are only very slightly inferior to thoseof white cast iron of the compositions commonly used in makingconventional malleable iron. The relatively high silicon content of thismaterial undoubtedly measurably contributes to these satisfactoryfeeding characteristics. As a result, sound castings of various shapesand sizes can be readily formed. In casting many articles thecast-to-clean ratio can be made equal to that of conventional malleableiron by the addition of small quantities of an exothermic risercompound.

Castings of this ferrous base metal can be successfully produced ingreen sand molds, dry sand molds and shell molds with no apparentvariation in results. Unlike white cast iron, the metal exhibits notendency to mottle when poured into shell molds. Also, the prevention offlake graphite formation is not a serious problem as is true withnodular iron. Another very important consideration is the fact that thecondition of cope side segregation of graphite nodules, which frequentlyis present in nodular iron castings, does not occur in the ferrous metaldescribed herein. Homogeneous microstructures are obtained in castingsof all sizes.

When this metal was made into test castings having section thicknessesranging from A1. inch to several inches, there was no greater tendencyfor carbide to form in the thin sections than in the larger sections,even though the size of the graphite nodules was somewhat reduced.

Moreover, the machineability of this ferrous metal, either in theas-cast condition or after heat treatment, appears to be entirelysatisfactory. When compared with pearlitic malleable iron, it was foundthat identical turning speeds and feed rates may be used, while drillingcast metal is somewhat less than in pearlitic malleable Since the'castmetal produced by our process may be annealed at temperatures in theorder of 1350 F. to provide a ferritic matrix, it .is possible for asingle foundry using the same base iron to produce all of the partscurrently formed from both ferritic and ,pearlitic malleable iron.Moreover, the increased strength resulting from normalizing andquenching and tempering treatments, as well as the high elastic modulusof the metal, permits it to be used in forming articles which areconventionally forged from plain carbon steel.

It should 'be noted that this cast ferrous metal requires no costly orexplosive addition agents, injection apparatus, or extensive heattreatment. Of course, there is no problem with regard to clogging ofinjection-tubes or controlling feed rates of injected material. Also,since an injection operation is not used, there is no reduction intemperature caused by such a procedure, and speed in the preparation ofthe metal is not an important factor. Late ferrosilicon additions arenot required to reduce the chill of the metal. Furthermore, unlike someof the upgraded cast irons heretofore made, a dry, granular slag is notformed during production of the metal and hence does not present anyremoval problems Likewise, it is unnecessary to de-sulfurize the metalor to use a base metal having a very low sulfur content. It is also notnecessary to employ a basic or neutral-lined ladle. Despite these facts,however, the outstanding mechanical properties of the new metal may bevaried appreciably by short and inexpensive heat treating procedures toprovide a diversity of useful products.

While the present invention has been described by means of certainspecific examples, it will be understood that the scope of the inventionis not to be limited thereby except as defined in the following claims.

We claim:

1. A method of producing a ferrous metal casting having a high modulusof elasticity, tensile strength and yield strength in the as-castcondition, said method com prising forming a melt which would solidifywith an essentially White iron microstructure in the absence of boron,said melt comprising 1% to 2.5% carbon, 1.5%

to 3.2% silicon, manganese not in excess of 1.15%,

0.001% to 0.05% boron and the balance substantially all iron,superheating said melt to a temperature of about 2900 F. to 3100 F. fora period of time sufficient to insure that castings produced therefromhave a microstructure substantially free of flake graphite with freecarbon predominantly in the form of compacted graphite, and subsequentlypouring said melt at a temperature of about 2600 F. to 2800 F. into amold.

2. A method of producing a ferrous metal casting having a high modulusof elasticity, tensile strength and yield strength in the as-c-astcondition, said method comprising forming a melt which would solidifywith an essentially white iron microstructure in the absence of boron,said melt comprising approximately 1% to 2.5 carbon, 1.5% to 3.2%silicon, manganese not in excess of 1.15%, and the balance substantiallyall iron, superheating said meltto a temperature of about 2900 F. to3100" F. for a short period of time suflicient to insure that castingsformed from said melt have an as-cast microstructure substantially freeof flake graphite with free carbon predominantly in the form ofcompacted graphite, thereafter tapping said melt into a ladle at atemperature of 2700 F. to 3000 F., inoculating the melt with boron in anamount suflicient to provide the melt with a boron content of about0.001% to 0.05%, and subsequently pouring said inoculated melt at atemperature of about 2600 F. to 2800 F. into a mold.

3. A method of producing a ferrous metal casting 1 0 having a modulus ofelasticity of ,at least 27.5- 010 p.s.i., said method comprising meltingtogether a mixture of plain low carbon steel and white cast iron in apro of about 2750 F. to 3000 F. and subsequently pouring said melt at atemperature of about 2600 F. to 2800 F. from said ladle into a mold.

4. A method of producing a ferrous metal casting having a modulus ofelasticity of at least 27.5 X 10 .;p.s.i., said method comprisingmelting together a mixture of plain low carbon steel and white cast ironin a proportion such that the resultant melt comprises about, 1% to to2.5% carbon, 1.5% to 2.8% silicon, manganese not in excess of 1.15sulfur not in excess of 0.5% and the balance substantially all iron,superheating said melt to a temperature of about 2900 F. to 3100 F. fora short period of time sufficient to insure that castings formed fromsaid melt have an as-cast microstructure substantially free of flakegraphite with free carbon predominantly in the form of compactedgraphite, inoculating said melt with boron in an amount suflicient toconstitute approximately 0.001% to 0.02% of the melt, and subsequentlypouring said melt at a temperature of about 2600 F. to 2700 F. into amold.

5. A method of producing a ferrous metal casting having a modulus ofelasticity of at least 27.5)(10 p.s.i., said method comprising forming amelt which would solidify with an essentially white iron microstructurein the absence of boron, said melt consisting essentially of about 1.5%to 1.9% carbon, 2% to 2.6% silicon, 0.3% to 1.15% manganese, 0.001% to0.02% boron, 0.05% to 0.15% sulfur and the balance substantially alliron, superheating said melt to a temperature of about 2900 F. to 3000F. for a period of time suflicient to insure that castings producedtherefrom have an as-cast microstructure substantially free of flakegraphite with free carbon predominantly in the form of compactedgraphite, tapping said melt into a ladle, and subsequently pouring saidmelt at a temperature of about 2600 F. to 2700 F. from said ladle into amold.

6. A method of producing a ferrous metal casting having a modulus ofelasticity of at least 27.5 10 p.s.i., said method comprising forming amelt which would solidify with an essentially white cast ironmicrostructure in the absence of boron, said melt consisting essentiallyof about 1.5% to 1.9% carbon, 2% to 2.6% silicon, 0.001% to 0.015%boron, manganese not in excess of 1.15 sulfur not in excess of 0.5% andthe balance substantially all iron, superheating said melt to atemperature of about 2900 F. to 3000 F. for a short period of timesufficient to insure that castings formed from said melt have an as-castmicrostructure substantially free of flake graphite with free carbonpredominantly in the form of compacted graphite, lancing said melt,thereafter tapping said melt into a ladle and subsequently pouring saidlanced melt at a temperature of about 2600 F. to 2700 F. from said ladleinto a mold.

7. A method of producing a ferrous metal casting having a modulus ofelasticity of at least 27.5 10 p.s.i., said method comprising meltingtogether a mixture of plain carbon steel and boron-containing white castiron, the ratio of said steel to said white cast iron being such as toprovide a melt consisting of about 1.5 to 1.9% carbon, 2% to 2.6%silicon, 0.005% to 0.02% boron, 0.3% to 1.15 manganese, sulfur not inexcess of 0.03% and the balance substantially all iron, lancing saidmelt;

with a dry gas to produce turbulence of said melt, superheating the meltat a temperature of about 2900 F. to 3000 F. for a period of timesufiicient to insure that castings formed from said melt have an as-castmicrostructure substantially free of hypereutectoid iron carbide andType D flake graphite with free carbon predominantly in compacted form,tapping said lanced melt into a ladle at a temperature of 2750 F. to3000 F., subsequently pouring said melt from said ladle at a temperatureof about 2600 F. to 2700 F. into a mold.

8. A method of producing a ferrous metal casting having a modulus ofelasticity of at least 27.5 10 p.s.i., said method comprising meltingtogether in a furnace a mixture of plain carbon steel andboron-containing white cast iron, the ratio of said steel to said whitecast iron being such as to provide a melt consisting of about 1.5% to1.9% carbon, 2% to 2.6% silicon, 0.005% to 0.015% boron, 0.3% to 0.8%manganese, sulfur not in excess of 0.03% and the balance substantiallyall iron, lancing said melt while in said furnace with a dry gas toproduce turbulence of said melt, superheating the melt at a temperatureof about 2900" F. to 3000 F. for a short period of time sufiicient toinsure that castings formed from said melt are substantially free ofhypereutectoid iron carbide and Type D flake graphite with free carbonpredominantly in compacted form, tapping said lanced melt into a ladleat a temperature of 2750" F. to 3000 F., inoculating the tapped meltwith tellurium in an amount equal to approximately 0.001% to 0.01% ofthe weight of the melt, and subsequently pouring said inoculated meltfrom said ladle at a temperature of about 2600 F. to 2700 F. into amold.

References Cited in the file of this patent UNITED STATES PATENTS IhrigJune 12, 1956

1. A METHOD OF PRODUCING A FERROUS METAL CASTING HAVING A HIGH MODULUSOF ELASTICITY, TENSILE STRENGTH AND YIELD STRENGTH IN THE AS-CASTCONDITION, SAID METHOD COMPRISING FORMING A MELT WHICH WOULD SOLIDIFYWITH AN ESSENTIALLY WHITE IRON MICROSTRUCTURE IN THE ABSENCE OF BORON,SAID MELT COMPRISING 1% TO 2.5% CARBON, 1.5% TO 3.2% SILICON, MANGANESENOT IN EXCESS OF 1.15%, 0.001% TO 0.05% BORON AND THE BALANCESUBSTANTIALLY ALL IRON, SUPERHEATING SAID MELT TO A TEMPERATURE OF ABOUT2900*F. TO 3100*F. FOR A PERIOD OF TIME SUFFICIENT TO INSURE THATCASTINGS PRODUCED THEREFROM HAVE A MICROSTRUCTURE SUBSTANTIALLY FREE OFFLAKE GRAPHITE WITH FREE CARBON PREDOMINANTLY IN THE FORM OF COMPACTEDGRAPHITE, AND SUBSEQUENTLY POURING SAID MELT AT A TEMPERATURE OF ABOUT2600*F. TO 2800*F. INTO A MOLD.